With the ongoing trend toward smaller, faster, and higher performance electrical components such as processors used in computers, routers, switches, etc., it has become increasingly important for electrical interfaces along electrical paths to also operate at higher frequencies and at higher densities with increased throughput.
In a traditional approach for interconnecting circuit boards, one circuit board serves as a back-plane and the other as a daughter board. The back-plane typically has a connector, commonly referred to as a header, that includes a plurality of signal pins or contacts which connect to conductive traces on the back-plane. The daughter board typically has a connector, commonly referred to as a receptacle connector, that also includes a plurality of contacts or pins. Typically, the receptacle connector is a right angle connector that interconnects the back-plane with the daughter board so that signals can be routed between the two. The right angle connector typically includes a mating face that receives the plurality of signal pins from the header on the back-plane and contacts that connect to the daughter board.
At least some board-to-board connectors are differential connectors wherein each signal requires two lines that are referred to as a differential pair. For better performance, a ground contact is associated with each differential pair. The receptacle connector typically includes a number of modules having contact edges that are at right angles to each other. The modules may or may not include a ground shield. As the transmission frequencies of signals through the receptacle connector increases, it becomes more desirable to maintain a desired impedance through the receptacle connector to minimize signal degradation. A ground shield is sometimes provided on the module to reduce interference or crosstalk. In addition, a ground shield may be added to the ground contacts on the header. Improving connector performance and increasing contact density to increase signal carrying capacity without increasing the size of the receptacle connector or header is challenging.
Some older connectors, which are still in use today, operate at speeds of one gigabit per second or less. By contrast, many of today's high performance connectors are capable of operating at speeds of up to ten gigabits or more per second. As would be expected, the higher performance connector also comes with a higher cost.
U.S. Pat. No. 6,808,420, granted to the applicant of the present application on Oct. 26, 2004, discloses an electrical connector comprising a connector housing holding signal contacts and ground contacts in an array organized into rows. Each row includes pairs of the signal contacts and some of the ground contacts arranged in a pattern, wherein adjacent first and second rows have respective different first and second patterns.
U.S. Pat. No. 6,379,188, granted on Apr. 30, 2002, shows an electrical connector for transferring a plurality of differential signals between electrical components. The electrical connector is made of modules that have a plurality of pairs of signal conductors with a first signal path and a second signal path.
Electrical connectors according to the prior art comprise a plurality of contacts embedded in a plastic housing. FIG. 1 shows a plurality of mating contacts 3 in such an electrical connector represented without the plastic housing. Each of the mating contacts 3 is electrically connected to a corresponding mounting contact 6 by a conductor 5. The plurality of conductors 5 connecting the mounting contacts 6 with the corresponding mating contacts 3 arranged on one of the rows, constitutes a so-called lead frame, an example of which is represented in FIG. 2.
FIG. 3 shows a cross-sectional view of the plurality of conductors 5 shown in FIG. 1, taken along one of lines A-A, B-B or C-C. In the electrical connector according to the prior art, the plurality of conductors 5 have electrical characteristics, which may vary depending on the position of a particular conductor within the electrical connector. Indeed, the conductors 5 located in outer regions of the electrical connector, which are identified in FIG. 3 by the conductors 5 represented in black, have electrical characteristics that vary from the electrical characteristics of the conductors 5 arranged in inner regions of the electrical connector, which are represented by the conductors 5 in FIG. 3 in white. In particular, the total capacitance of the individual conductors 5 arranged in the outer regions of the electrical connector is typically lower than the total capacitance of the conductors 5 located in the inner regions of the electrical connector. This phenomenon is due to the fact that the conductors 5 in the outer regions do not have neighbors on one side, which results in non-uniform electrical characteristics. These non-uniform electrical characteristics may lead to a degradation of the signals transmitted by the electrical connector.